On Tue, Dec 22, 2020 at 08:28:30AM +1100, Steven D'Aprano wrote:
> An alternative, which may be better or worse but is probably worth
> considering, is to create your own wrapper proxy for True and False,
> then use that.
It has come to my attention that my post may have been unclear. I
don't mean to suggest that the *consumers* of the library be responsible
for changing all uses of True/False bools into the special proxies.
Rather, I meant that the *library itself* should internally replace
True/False with its own custom objects that hash and compare
differently. Here's an untested sketch of a solution:
```
class Boolean(object):
# Proxy the genuine True and False bools.
def __init__(self, obj):
self._obj = obj
def __bool__(self):
return self._obj
def __eq__(self, other):
return self is other
def __hash__(self):
return 17 + self._obj
TRUE = Boolean(True)
FALSE = Boolean(False)
class MyDict(dict):
def __getitem__(self, key):
if key is True:
key = TRUE
elif key is False:
key = FALSE
return super().__getitem__(key)
```
and similar for `__setitem__` etc.
The caller of the library doesn't need to know that their data
containing True/False bools are silently replaced by TRUE/FALSE inside
the mapping. They just use True and False in their code as normal and it
should all just work.
Subclassing dict is sometimes tricky to get right, you might find it
easier to subclass collections.UserDict.
--
Steve
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